POWER STEERING DEVICE FOR AN AUTOMOBILE

Abstract: An electrical power steering device for an automobile is disclosed. The device has a steering motor (1), transmitting means (4) having two transmitting portions rotating in the opposite direction respectively, by the steering motor, coupling means (5) coupling one of the two transmitting portions to at least one of the steering shaft (102) and the steering link, and switching means (6) applying a driving signal to the steering motor (4) when the steering wheel (101) rotates and a selective coupling signal to the coupling means (5) corresponding to the steering direction of the steering wheel (101).

Description: POWER STEERING DEVICE FOR AN AUTOMOBILE Field of the Invention The present invention relates to a power steering device for an automobile, and more particularly to an electrical power steering device which has a steering motor connected to one of the steering link or the steering shaft, and switching means installed on one of the steering shaft or the steering wheel to apply driving signals to the steering motor. Background of the invention Conventional power steering devices for automobiles currently used are mainly oil-hydraulic types. These types of power steering devices have an oil pump as a hydraulic power unit, an oil-hydraulic actuator converting oil pressure from the oil pump into mechanical strength to generate steering force, a control unit controlling the operation of steering by openning or closing the passage between the oil pump and the actuator, and a number of additional components to ensure the operational accuracy. Therefore, these power steering devices require comparatively complicated mechanical structure, large mounting space, increase of weight, and high production cost. Furthermore, a regular replenishment of oil is required in order to maintain its best performance. Consequently, various kinds of electrical power steering devices are known which replace the oil pump and the actuator by a steering motor. Japanese Patent Publication No. 83-202803 and No. 84-70257 disclose typical ones of these kinds. These power steering devices generally have a steering motor connected to the steering link or to the steering shaft, a torque sensor detecting the torque of the steering wheel, a speed sensor detecting the running speed of a car, and a control unit changing the torque of the steering motor in accordance with the output from each sensor. However, most of these electrical power steering devices usually have some fatal disadvantages. First of all, they have a high probability of malfunction such as for example unintended steering against drivers' intention, mostly due to the variation of voltage on the circuit, which is generated from the power source and/or the torque sensor. Secondly, they have a high probability of damage to the circuit due to the resistances used for changing the torque of the steering motor, and in case of such damage, the steering capability may be lost, bringing about extreme danger. Thirdly, they have a structural difficulty in returning the steering wheel and the steering shaft to the straight direction when the steering is over, because the steering motor rotates together with the steering wheel, otherwise an additional circuit should be provided for this purpose. Due to the drawbacks still unsolved, the electrical power steering devices have not been widely used in spite of their simple structure and light weight. The inventor disclosed an electrical power steering device by U.S. Patent Application No. 08/097,709 and No. 08/117,239. This electrical power steering device is believed to succeed in solving most of the problems described in the above, but a delay in steering response time occurred due to the inertia rotation of the steering motor. Accordingly, the inventor has studied to acquire an imediate steering response in the electrical power steering device, and as a results, found that this imediate steering reponse can be obtained by making the steering motor rotate in one direction all the time, and changing the structure of transmission between the steering motor and the steering shaft. SUMMARY OF THE INVENTION Therefore, it is an essential object of the present invention to provide an electrical power steering device which is free of the above-mentioned drawbacks and has an imediate steering response. It is another object of the present invention to provide an electrical power steering device which is capable of shifting its steering mode, that is, from manual steering mode to power steering mode in accordance of a driver's intention or the running speed of a car. According to the present invention, there is provided an electrical power steering device for an automobile, which comprises a steering motor, transmitting means having two transmitting portions rotating in the opposite direction respectively, by the steering motor, coupling means coupling one of the two transmitting portions to the steering shaft, and switching means applying a driving signal to the steering motor when the steering wheel rotates and a selective coupling signal to the coupling means corresponding to the steering direction of the steering wheel. BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic view of the present invention. FIG. 2 to FIG 4 are a schematic view illustrating an embodiment of the transmitting means and the coupling means according to the present invention. FIG. 5 is a perspective view illustrating an embodiment of the switching means according to the present invention. FIG. 6 is a longitudinally sectioned view taken on line A- A' of FIG. 5 FIG. 7 is a sectioned view taken on line B-B' of FIG. 6 FIG. 8 is a block diagram showing an example of a circuit with a function to make the steering properly heavy in proportion to the running speed of a car DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 of the drawings, there is shown a power steering device according to the present invention. A steering wheel 101 is connected to a steering shaft 102, and the steering shaft 102 is connected to a steering link 103. In the present invention, there is provided a steering motor 1 driven to rotate when the steering wheel 101 rotates, transmitting means 4 having two transmitting portions 2,3 rotating in the opposite direction respectively, by the steering motor 1, coupling means 5 coupling one of the two transmitting portions 2,3 to the steering shaft 102, and switching means applying a driving signal to the steering motor 1 and a selective coupling signal to the coupling means 5 corresponding to the steering direction of the steering wheel 101. FIG. 2 to FIG. 4 show the first embodiment of the transmitting means and the coupling means according to the present invention. The transmitting means have a driving gear 11 connected to the steering motor, and two transmitting portion 2, 3 rotating in the opposite direction, respectively, driven to rotate by the driving gear 11. Transmitting portion 2 has an even number of following gears 12, 13 connected to driving gear 11, while transmitting portion 3 has an odd number of following gear 14 connected to driving gear 11. Thus, following gear 13 of transmitting portion 2 rotates in the same direction as that of driving gear 11, while following gear 14 of transmitting portion 3 rotates in the opposite direction as that of driving gear 11. The driving gear 11 and the following gears 12, 13, 14 are installed in a gear housing 15 which can swing arornd the axis of the driving gear 11 within a predetermined stroke, as shown in Fig. 3 and Fig. 4. According to the swinging direction of gear housing 15, one of the following gear 13, 14 is connected to the steering shaft 102 at each end of its swinging stroke, and thus, the steering shaft 102 is driven to rotate in a normal or a reverse direction. A projected portion 16 is formed integrally with the gear housing 15, and two solenoids 17, 18 is installed at each end of the swinging stroke of the projected portion 16. The switching means 6 apply an electrical current to one of these two solenoids 17, 18, corresponding to the steering direction of the steering wheel. Thus, the projected portion 16 and the gear housing 15 swing toward one of the solenoide 17, 18. As a result, according to the steering direction of the steering wheel, one of the following gears 13, 14 is coupled to the steering shaft 102, and the steering shaft 102 is driven to rotate in a normal or a reverse direction. An elastic member 19 is preferrably installed between the projected portion 16 and the body. This elastic member 19 makes the gear housing 15 maintain its neutral position(the position shown in Fig. 2) when the steerin wheel does not rotate. The above described transmitting means and the coupling means can make the steering motor rotate in one direction all the time, regardless of the steering direction, and all the problems concerned with the inertia rotation of the steering motor, such as a delay in the steering response time, can be solved. FIG. 5 to FIG. 7 show one embodiment of the switching means according to the present invention, in which FIG. 5 is a perspective view, FIG. 6 is a longitudinally sectioned view taken on line A- A' of FIG. 5, and FIG. 7 is a sectioned view taken on line B-B' of FIG. 6. In this embodiment, a hollow cylindrical outer shaft 31 is rotatably disposed in a shaft housing 33, and a cylindrical inner shaft 32 is rotatably disposed in the outer shaft 31. The inner shaft 32 is connected to a steering wheel 34 at the upper end, and the outer shaft 31 is connected to a steering link (not shown) at the lower end. The inner shaft 32 has a projected portion 36, and the outer shaft 31 has an openning 37 for guiding the projected portion 36 to move therealong. Thus, the moving stroke of the inner shaft 32 is restricted within the length of the openning 37. Two switches 38, 39 are installed on each end of the openning 37 so that the projected portion 36 can contact with one of these two switches 38, 39 when moving. The switches 38, 39 have identical construction, and any of them drives the steering motor(not shown) to rotate in one direction, when contacted by the projected portion 36. Also, when one of these two switches 38, 39 is contacted by the projected portion 36, corresponding to the steering direction of the steering wheel, the contacted switch 38 or 39 applies an electrical current to one of the two solenoids 17,18 and thus, one of the following gear 13, 14 is coupled to the steering shaft 102. As a result, the steering shaft 102 can be rotate in the direction corresponding to the steering direction of the steering wheel. An elastic member 40 is installed between the outer and the inner shaft 31, 32 so that the inner shaft 32 can stay at and return to the initial position "PI" which has about equal distance from each of those two switches 38, 39. Reference Number 43, 44, 45, and 46 are bearings. 1° accordance with another feature of the present invention, a torsion coil spring 41 is provided. This torsion coil spring 41 winds around the upper portion of the inner shaft 32, piercing through a hole 42 of the inner steering shaft 32. The upper and lower end of the torsion coil spring 41 is fixed to the shaft housing 33. Therefore, when the steering wheel 101 and the inner steering shaft 32 is rotating, the torsion coil spring 41 accumulates torsional stress corresponding to the rotated angle. Consequently, when the steering wheel 101 is released, the projected protion 36 continues to move toward the other one of the switches 38, 39, and the steering wheel 101 returns to the straight direction, until no more torsional stress is left. Especially, it is apparently anticipated that this restoring movement takes place even in the state when a car is standing completely still, to say nothing of the state when a car is just driving out of a corner. FIG. 8 is a block diagram which shows an example of a circuit with a function to make the steering properly heavy in proportion to the running speed of a car. This circuit has two pressure sensors installed at each of the two switches 38, 39 and detecting the pressure applied to the two switches 38, 39, a speed sensor detecting the running speed of a car, and a control unit applying the driving signal to the steering motor only when the pressure value detected at one of the two pressure sensors exceeds an effective pressure value determined by the current running speed detected at the speed sensor. The effective pressure value increases in proportion to the running speed of a car. Therefore, the faster a car runs, the more power is required to get a steering. That is, the steering becomes properly heavy as the speed of a car increases, thereby acquiring more enhanced safety. Various changes and modifications may be made within the scope of the inventive concept.

Claims: What is claimed is: 1. In an electrical power steering device including a steering wheel connected to one end of a steering shaft, and a steering link connected to the other end of said steering shaft, comprising: a steering motor; transmitting means having two transmitting portions rotating in the opposite direction respectively, by said steering motor; coupling means coupling one of the two transmitting portions to at least one of said steering shaft and said steering link; and, switching means applying a driving signal to said steering motor when said steering wheel rotates and a selective coupling signal to said coupling means corresponding to the steering direction of said steering wheel. 2. The electrical power steering device of claim 1, wherein, said transmitting means comprising: a driving gear connected to said steering motor; one of said two transmitting portions having an even number of following gears, one of which connected to said driving gear; the other one of said two transmitting portions having an odd number of following gear(s), one of which connected to said driving gear; a gear housing rotatably accomodating said driving gear and said following gears, and swinging around the axis of said driving gear in a predetermined swinging stroke. 3. The electrical power steering device of claim 2, wherein said coupling means comprising: a projected portion formed integrally with said gear housing; two solenoids installed at each end of the swinging stroke of said projected portion, said projected portion and said gear housing swinging toward one of said two solenoids when said coupling signal is applied by said switching means; and a elastic member installed between said projected portion and a body frame, said elactic member making said projected portion and said gear housing maintain a position in which said projected portion does not contact with any of said two solenoids. 4. The electrical power steering device of claim 1 and claim 3, wherein, said steering shaft comprises; a hollow cylindrical outer shaft rotatably disposed in a shaft housing, the lower end of which being connected to said steering link, a cylindrical inner shaft rotatably disposed in said outer shaft, and said switching means comprises; a projected portion formed on said inner shaft, and moving along an openning formed on said outer shaft, thereby the moving stroke of which being restricted within the length of said openning, and two switches installed at each end of said openning, and applying driving signals to said steering motor and a selective coupling signal to one of said two solenoids corresponding to the steering direction of said steering wheel, when contacted by said projected portion. 5. The electrical power steering device of claim 4, further comprising, an elastic member, one end of which is fixed to said inner shaft, while the other end is fixed to said outer shaft, thereby making said projected portion stay at and return to a position which has about equal distance from each of said switches. 6. The electrical power steering device of claim 4, further comprising, a torsion coil spring winding around said inner shaft, the middle portion of said torsion coil spring being fixed to said inner shaft, and the upper and lower portions of said torsion coil spring being fixed to said shaft housing, thereby returning said steering wheel to the straight direction when a steering is over. 7. The electrical power steering device of claim 4, further comprising, two pressure sensors installed at each of said two switches and detecting the pressure applied to said two switches, a speed sensor detecting the running speed of a car, and a control unit applying a driving signal to said steering motor only when the pressure detected at said pressure sensors exceeds an effective pressure determined by the current running speed detected at said speed sensor, wherein said effective pressure is proportion to the running speed of a car.

Inventors: HONG SOON YOUNG, HONG, SOON, YOUNG
Applicants: HONG SOON YOUNG, HONG, SOON, YOUNG
Application year: 1994
Main classification: B62D5
IPC codes: B62D5